This invention relates to multicylinder reciprocating compressors for use in refrigeration systems. More particularly, this invention relates to such compressors wherein the reexpansion volume of each cylinder is optimized.
Prior art multicylinder reciprocating compressors have generally used a unitary valve plate to cover all of the cylinders of the compressor. Such valve plates are generally comprised of a single, unitary, relatively massive steel or cast iron plate which is sealed to the crankcase of the compressor by means of a unitary head gasket. In the compressor environment, the cylinder clearance is generally referred to as the distance within the cylinder between the top of the piston and the valve plate when the piston is at the farthest extension of its stroke, commonly referred to as the top dead center position. Such prior art compressor head gaskets are selected so that the minimum cylinder clearance of the piston having the maximum extension is greater than a predetermined desired limit. Thus, in such prior art arrangements, the maximum cylinder clearance of the pistons, due to manufacturing tolerances, is uncontrolled. It is desired to hold cylinder clearance to a minimum since the compressor capacity and efficiency are thereby optimized. In operation, as the piston reciprocates within the cylinder, the volume of gas which occupies the clearance volume of the cylinder is repeatedly compressed and expanded without resulting in any useful work. It is, therefore, desired to minimize the cylinder clearance volume and to thereby minimize the lost work by providing a compressor wherein the cylinder clearance of each individual cylinder is adjusted during assembly of the compressor to minimize the cylinder clearance volume.
In one prior U.S. Pat. No. 2,647,683, cylinder clearance has been adjusted by means of an adjustable plug which is threadedly received in the compressor cylinder to provide a predetermined cylinder clearance within the compressor. However, this prior art structure is relatively complicated and is therefore relatively expensive to manufacture. It is therefore desired to provide a multicylinder compressor with an adjustable cylinder clearance volume which is structurally simple and inexpensive to manufacture.
In another U.S. Pat. No. 2,613,870, the adjustable cylinder clearance volume has been provided by means of a thin valve plate which may be deformed to provide more or less "dishing". This prior art structure is also relatively complicated and uses several parts to perform this "dishing" function and is therefore undesirable. It is therefore desired to provide a reciprocating compressor wherein no extra parts are used to provide an adjustable cylinder clearance volume.